Principled Shader inputs
Just ignore the input list index values. Treat the input list as a dictionary.

shPrin.inputs['Specular'].default_value = 0.015
shPrin.inputs['Sheen Tint'].default_value = 0.2
shPrin.inputs['IOR'].default_value = 1.8


If you know an index and want to know the name -

&gt;&gt;&gt; shPrin.inputs[11].name
'Sheen Tint'


And to list all the available names -

for i in shPrin.inputs:
    print(i.name)